The present invention relates to elevator systems. In particular, the present invention relates to power system for driving a plurality of elevator hoist motors.
The power demands for operating elevators range from highly positive, in which externally generated power is used at a maximal rate, to negative, in which the load in the elevator drives the motor so it produces electricity as a generator. This use of the motor to produce electricity as a generator is commonly called regeneration. On average, if all the passengers who rise up through a building on an elevator also return down through the building on the same elevator, the average power required to run the system would be zero, but for frictional losses, electrical conversion losses, and power drawn by accessory equipment (e.g., lighting). However, this typically does not occur since most elevators are dispatched based on efficiency, and power management considerations are often ignored. For example, if two or more elevators are dispatched at the same time, the overlapping current transients from the associated motors results in a significant power demand on the power supply. Thus, the deliverable power from the power supply must be very large to avoid an overload condition if all elevators start at the same time.
In addition, conventional multi-elevator power systems typically include a dedicated power bus and power converter for each hoist motor. Consequently, the power consumed by each hoist motor is independent of the power consumed by the other hoist motors of the multi-elevator power system. This results in inefficient use of the power supply. For example, a significant amount of energy generated by each of the hoist motors during regeneration may need to be dissipated as waste heat if negative power demands exceed the storage capacity of the power system. This not only is wasteful of the generated electricity, but also adds more waste in the requirement for air conditioning to keep excessive heating from occurring.